According to Princeton University researchers, Deborah Son Holoien and Susan Fiske, when people want to appear warm they will downplay their competence; when people want to appear competent they will downplay their warmth.
Anecdotal evidence from a friend of iamnotthebabysitter.com (who wants to remain anonymous) shows that at least the former is true…she just admitted to me that she downplays her competence to appear friendly. She is convinced that women are more likely to do this, and feels that she does this because she has learned that, being blonde and a woman, she meets expectations better if she downplays her intelligence. People seem more comfortable if they know what to expect and get what they expect. My friend is also convinced that I do it.